Many different types of manually removable bottle caps have been known heretofore. Such caps include tear tabs of various designs as well as sealing elements bonded to the undersurface of the top of the cap. Said tear tab serves as a lever arm, so that during the tearing operation, forces tending to pull the cap from the bottle are exerted along the top surface of the cap. At the beginning of the tearing operation, the skirts grips the bottle so that the forces exerted by the tear tab acts to tear the cap along the score lines. As the cap is torn, however, the grip of the skirt on the bottle is relaxed, when the grip of the skirt is relaxed enough, the cap is lifted from the bottle neck.
Such sealing caps must be constructed so that they provide an efficient seal for the opening, but are still easy to remove by manually tearing up a flap projecting from the cap which, for this purpose, cooperates with tear-off indications extending across the top of the cap. In order to achieve the necessary seal, such caps are provided with a seal abutting the mouth of the bottle. Furthermore, the seal should be constructed so that it holds the cap together in one piece after it has been torn up and removed from the opening, so that if necessary it can be used again to temporarily close the bottle opening.
The few bottle caps utilized heretofore which do have a capability of being reused, generally are not sufficiently released from their claw-grip around the neck during the tearing operation, i.e. the lower part of the cap which during the sealing operation is bent around the neck of the container opening is not sufficiently released so that the cap after tearing can easily be drawn from the opening. If this release cannot be achieved special manipulations are necessary for removing of the cap, which is made more difficult by the relatively sharp edges obtained by the tearing operation. Thus, said sharp edges may easily result in cuts or other damages. This problem is particularly noticeable with caps employed on openings having relatively large diameters and is even more pronounced if the sealing element consists of an insert covering the total undersurface of the cap and which, with the object of providing an efficient re-sealing, is constructed so that it is retained unbroken during the tearing operation. This type of sealing element also contributes to a certain extent to the clawgrip mentioned above. Furthermore, for technical reasons during manufacturing of said caps it has previously been necessary to use a seal covering the whole undersurface of the cap in order to eliminate any risk of corrosion which might otherwise easily occur along the tear lines. Normally the cap blank is provided at least on one surface with a layer of a corrosion-resistant varnish before the tear-off indications are applied, but said layer is obviously damaged when the tear-off indications are employed by punching or the like. Resulting corrosion risks could of course be avoided by subsequent re-varnishing of the cap, but this in turn involves a troublesome additional stage in the production line and instead the seal has been allowed to cover the entire undersurface of the cap. The disadvantage of this is of course a considerably increased cost for the material for the seal itself, although the effective sealing surface in fact need only be within a narrow region located over the neck surrounding the opening of the bottle.